Israeli military spokesman Lt. Col. Peter Lerner said the rocket fire struck near Israel’s northern border and the military responded with artillery fire toward the apparent source in southern Lebanon. There were no reports of injuries.

Lebanese security officials said militants fired four rockets around 6 a.m. (0300 GMT) and the Israelis retaliated by firing about a dozen artillery shells on the area. Lebanese troops and United Nations peacekeepers later began searching the area, said officials who spoke on condition of anonymity because they were not authorized to speak to journalists.

That area in southern Lebanon is a stronghold of the Shiite militant group Hezbollah, which has battled Israel numerous times. However, past fire from Lebanon has been blamed on radical Palestinian factions in the area and Hezbollah has not been involved in the ongoing offensive.

Lerner said Israel has suspected that Lebanese militants may try to join the fray as Israel exchange fire with Islamic Hamas militants in Gaza. However, he said it was still unclear whether Friday’s attack was “symbolic or something more substantial.”

Gaza militants already have fired more than 550 rockets against Israel in the four-day offensive. Israel’s “Iron Dome” defense system has intercepted most of those aimed at major cities but some have slipped through.

On Friday, one such rocket struck a gas station in the southern city of Ashdod, setting off a large blaze and sending plumes of smoke into the air. Israeli media reported one person was seriously wounded in the blast.

Air raid sirens sounded once more across the country Friday, including for the first time in the northern city of Haifa.

In Gaza, an Israeli airstrike hit the home of a known Islamic Jihad leader. Gaza health officials said five people were killed in the strike, raising the death toll there to at least 90, including dozens of civilians.

Lerner said the military was doing its utmost to prevent civilian casualties, calling inhabitants ahead of time to warn of an imminent attack. He said Israeli forces also fire “non-explosive munitions” at roofs as a warning and looks for people to leave before destroying a structure.

A rocket struck a gas station Friday in the southern city of Ashdad sending a pillar of smoke in the air:

Israel launched the Gaza offensive to stop incessant rocket fire. The military says it has hit more than 1,100 targets already, mostly what it identified as rocket-launching sites.

He said it was Hamas itself that was responsible for the death of innocent bystanders by firing from heavily populated areas.

Israel’s military “uses its weapons to defend its civilians. Hamas uses its civilians to defend its weapons,” he said.